Bibcode
Luna, M.; Priest, E.; Moreno-Insertis, F.
Referencia bibliográfica
The Astrophysical Journal, Volume 863, Issue 2, article id. 147, 14 pp. (2018).
Fecha de publicación:
8
2018
Revista
Número de citas
2
Número de citas referidas
2
Descripción
Rotating magnetic structures are common in astrophysics, from vortex
tubes and tornadoes in the Sun all the way to jets in different
astrophysical systems. The physics of these objects often combine
inertial, magnetic, gas pressure, and gravitational terms. Also, they
often show approximate symmetries that help simplify the otherwise
rather intractable equations governing their morphology and evolution.
Here we propose a general formulation of the equations assuming
axisymmetry and a self-similar form for all variables: in spherical
coordinates (r, θ, ϕ), the magnetic field and plasma
velocity are taken to be of the form
{\boldsymbol{B}}={\boldsymbol{f}}(θ )/{r}n and
{\boldsymbol{v}}={\boldsymbol{g}}(θ )/{r}m, with
corresponding expressions for the scalar variables like pressure and
density. Solutions are obtained for potential, force-free, and
non-force-free magnetic configurations. Potential field solutions can be
found for all values of n. Nonpotential force-free solutions possess an
azimuthal component B ϕ and exist only for n ≥ 2
the resulting structures are twisted and have closed field lines but are
not collimated around the system axis. In the non-force-free case,
including gas pressure, the magnetic field lines acquire an additional
curvature to compensate for an outward pointing pressure gradient force.
We have also considered a pure rotation situation with no gravity, in
the zero-β limit: the solution has cylindrical geometry and twisted
magnetic field lines. The latter solutions can be helpful in producing a
collimated magnetic field structure; but they exist only when n < 0
and m < 0: for applications they must be matched to an external
system at a finite distance from the origin.
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